Abstract Acetate and formate anions along with the other major ions were determined in a 14-month wet-only precipitation study. The total formate/total acetate concentration ratio was 0.69 with the formate concentrations significantly smaller than reported in remote regions and the US. Presumably formic acid production is not favored under the dry conditions that prevail in this region of Greece. During the spring months, but not in the fall ones, generally greater concentrations were observed, indicating during this period significant biogenic sources. No rain fell in the summer months. Factor analysis indicated an association of the two weak acids with SO 4 2−and NO 3 −, two species commonly associated with anthropogenic activity. Acetic acid contributed 20% to the free acidity and formic acid 17%. However, their contribution to the total acidity was 10% for acetic and 0.7% for formic acid.